Drilling rigs used throughout the world for oil recovery operations include a rotary table which is powered by a draw works. A kelly having a rectangular outer configuration mates with and is rotated by a drilling rig rotary table. The lower end of the kelly includes threads for mating engagement with drill pipe thread. Accordingly, the drilling fig draw works rotates the rotary table, which rotates the kelly, which then rotates the drill pipe.
Those skilled in the petroleum recovery industry appreciate that the cost of recovering hydrocarbons can be significantly reduced by utilizing a workover rig or a snubbing unit to perform workover and/or snubbing operations. The utility of a drilling rig is thus increased by using this high cost rig almost exclusively for drilling operations. A workover rig, which practically may consist of a much smaller drilling rig, is thus frequently used for workover operations. A typical workover operation may involve the drilling or milling of a downhole packer or other tool out of a well. A workover rig can perform this operation at a fraction of the cost of utilizing a drilling rig.
A snubbing unit is similar to a workover rig, and typically has the additional capability of allowing the workover operation without "killing" the well. The snubbing unit typically has a raised work platform thirty feet or more off the rig floor. A snubbing unit thus does not require a derrick or draw works, and allows oilfield tubular goods to be made up at the raised work platform while high pressure drilling tools keep the well under pressure. A suitable snubbing unit may be used for snubbing in a kill string, for sand washing operations, for drilling through bridges, for drilling or milling packers or plugs, for fishing operations, or for pulling or running tubing in a cased well.
When conducting workover operations, it is typically not essential that the workover string continually be rotated in the wellbore. When pulling or running tubing, for example, the workover string is typically stationary as the upper tubular is threaded by a power tong to the stationary lower tubular. When conducting snubbing operations, however, the high well pressure increases the likelihood that a stationary workover string will become stuck in the wellbore. While snubbing operations have significant advantages compared to workover operations where the well is killed, a recognized disadvantage of a snubbing operation is that the workover string may become stuck in a wellbore. When this occurs, remedial operations to "unstick" the string can be very expensive and time consuming. In some instances, it is also desirable to rotate a work string during a conventional workover operation even when the well is killed.
The disadvantages of the prior art are overcome by the present invention. Improved techniques and equipment are hereinafter disclosed which allow the reliable and cost effective rotation of a workover string during the snubbing or workover operations. More particularly, the tool of the present invention allows for the rotation of the entire work string when making up or breaking apart a threaded joint at the well.